Tamper-proofing information included in documents, such as travel documents, IDs, birth certificates, certificates of insurance, permits, licenses, and the like is an important aspect of the document security industry. Many security features have been suggested to enable security personnel to identify tampering of important document data.
One common method is to print a one- or two-dimensional bar code on the document. The authentication is usually performed by creating a data set that includes the important data fields of a document. This data set is embedded in a bar code that is included in a document. By decoding the bar code, the embedded bar code data may be compared to data included in the data fields of the document.
Another protection method is to embed data into the security image design using digital watermarking, and print the watermarked image. During verification, data is extracted from a scanned watermark, and compared to the data printed on the document. Another popular method is to use the optical watermarks, such as scrambled images, or images based on shifting, displacing, rotating, or modulating the size of the security screen elements to match the variable data content. A portion of the data content may be static data.
Many of these methods are well known in the industry, and are often based on simple modifications of the halftone screen elements, making them easy to replicate by forgers using widely available desktop image editing software. Bar codes of all types are easily available through many web services, which generate bar code images based on the data entered on a web form. Some of these methods are based on technologies that are proprietary, non-standardized, and difficult to evaluate independently, thus failing the well-known adage that obscurity is not security. Some methods use custom made authentication tools, which have to be distributed to all verification locations. Accordingly, a need to tamper proof documents still exists. It is for these and other concerns that the following disclosure is presented herein.